1. Field of the Invention
The present invention relates to an ultrasonic flow switch which is operable based on a flow rate of a fluid which flows in a pipe.
2. Description of Related Art
A flow meter is used for accurately measuring a value of a flow rate of a fluid which flows in a pipe. For example, JP-A-2001-356032 discloses an ultrasonic flow meter having a sensor. The sensor can measure a flow rate of a fluid which flows in a pipe using an ultrasonic wave. In the sensor, two sleigh-like blades which project downward are formed. A sheet-like silicone gel is arranged between two blades. The sensor is fixed to an outer peripheral surface of a pipe by being fastened by a fastening band such that bottom sides of two blades are brought into contact with the pipe.
JP-A-2001-356032 describes that “the sensor can be stably fixed to a pipe, regardless of a position where the sensor is mounted, such as an upper side or a lower side of a horizontal part, a vertical part or an inclined part of the pipe, and can be stably fixed to pipes with almost all pipe diameters except pipe diameters equal to or less than a distance between the two sleigh-like blades”. However, in an actual ultrasonic flow switch, even when a sensor is fixed to a pipe having a size larger than the distance between the two sleigh-like blades, the position of an ultrasonic wave radiation surface of the sensor is not accurately determined.
Accordingly, it is difficult to adjust sensitivity of the sensor. Further, when the sensor is fastened by a fastening band with an excessively large strength for stabilizing the position of the ultrasonic wave emitting surface, the ultrasonic wave emitting surface may be damaged.
On the other hand, as in the case of controlling an operation state of a facility in a plant, there may be a case where an accurate value of a flow rate of a fluid which flows in a pipe is unnecessary and it is sufficient to detect whether or not the fluid flows in the pipe at a flow rate of a fixed value or more. In such a case, a flow switch which outputs an ON/OFF signal can be used instead of a flow meter. The flow switch is mounted on pipes having various outer diameters in a plant, for example. Accordingly, it is desirable that the flow switch can be stably mounted on pipes having various sizes.